Add GTest infrastructure

thirdparty/CMakeLists.txt

 add_subdirectory(KWSys)
+
+if(BUILD_TESTING)
+  add_subdirectory(GTest)
+endif()

thirdparty/GTest/CMakeLists.txt

+set(KWSYS_NAMESPACE adios2sys)
+set(KWSYS_USE_DynamicLoader ON)
+set(KWSYS_BUILD_SHARED OFF)
+if(NOT ADIOS_BUILD_SHARED_LIBS)
+  set(KWSYS_INSTALL_EXPORT_NAME adios2)
+  set(KWSYS_INSTALL_LIB_DIR ${CMAKE_INSTALL_LIBDIR})
+endif()
+
+add_subdirectory(adios2sys)
+
+# Add the include usage requirements for KWSys
+target_include_directories(adios2sys
+  INTERFACE ${CMAKE_CURRENT_BINARY_DIR}/adios2sys
+)

thirdparty/GTest/Readme.txt

+This is a copy of the upstream Google C++ test framework located at
+https://github.com/google/googletest. Do not make changes directly to this repo
+but instead to the upstream repository.  Update this copy of GTest by running
+the update.sh script.

thirdparty/GTest/update.sh

+#!/usr/bin/env bash
+
+set -e
+set -x
+shopt -s dotglob
+
+readonly name="GoogleTest"
+readonly ownership="Google Test Upstream <robot@adios2>"
+readonly subtree="thirdparty/GTest/googletest"
+readonly repo="https://github.com/google/googletest.git"
+readonly tag="release-1.8.0"
+readonly shortlog="true"
+readonly paths="
+"
+
+extract_source () {
+    git_archive
+}
+
+. "${BASH_SOURCE%/*}/../update-common.sh"